The present invention relates to a process for the production of aluminum silicate salt particles, and in particular, to a process for the production of ultrafine aluminum silicate salt particles having a high BET surface area and oil-absorbability.
Powders having a high BET surface area, and oil- and liquid-absorbability, are strongly required as anti-consolidation agents for deliquescence materials such as table salt and fertilizers, carriers for agricultural chemicals and insecticides, and lagging materials. In addition, the demand for such powders having a high surface area and low affinity of the second aggregation is rapidly growing for use as fillers for various materials including rubbers, plastics, paints, and inks.
The aforementioned term "oil-absorbability" may be defined as the capacity of a powdery sample to absorb large amounts of oil, e.g. linseed oil, yet remain in a powdery phase.
Silicic acid anhydride (silicon dioxide), silicic acid, calcium silicate, and synthetic calcium carbonate are mainly used as inorganic powders having relatively high BET surface area and oil-absorbability in the industrial fields.
The silicon acid anhydride can be prepared by a so called dry process, which process may be categorized into a "flame process" and an "arc process". In the flame process, silicic acid anhydride may be prepared by decomposition of halogenated silicic compounds by means of oxyhydrogen flame, or by thermal decomposition of organic silicon compounds. A typical reaction equation of the thermal decomposition process is as follows: EQU Si+2Cl.sub.2 .fwdarw.SiCl.sub.4 SiCl.sub.4 +H.sub.2 +O.sub.2 .fwdarw.SiO.sub.2 +HCl
In the arc process, a mixture of silica and coke is subjected to reduction by an arc and then to oxidation.
The silicic acid may be prepared by a so called wet process, in which sodium silicate is subjected to decomposition by an acid or an ammonium salt, or in which an alkaline earth metal salt derived from sodium silicate is subjected to decomposition by an acid. In addition, there is a so called organogel process, in which an organogel of silicon dioxide is converted to an aerogel in an autoclave. A typical reaction equation of the wet process is as follows: EQU Na.sub.2 O.multidot.mSiO.sub.2 +HCl+nH.sub.2 O.fwdarw.mSiO.sub.2 .multidot.nH.sub.2 O+NaCl
The calcium silicate may be prepared by a so called wet process, in which silicic acid and a milk of lime is reacted in the presence of high pressure steam, the pressure involved in this process being in the range of 4 to 14 kg/cm.sup.2. A typical reaction equation is as follows: EQU mSiO.sub.2 +Ca(OH).sub.2 +nH.sub.2 O.fwdarw.CaO.multidot.mSiO.sub.2 +nH.sub.2 O
The calcium silicate usually obtained in a conventional process, in which silicon compounds and calcium hydroxide are reacted in an autoclave, may be divided into tobermorite and xonotlite in accordance with its crystal configuration. The tobernorite and xonotlite calcium silicate may be produced under the condition of a pressure of 4 to 14 kg/cm.sup.2 and a reaction time of 8 to 12 hours, and a pressure of 14 to 20 kg/cm.sup.2 and a reaction time of 8 to 12 hours, respectively. These calcium silicate powders are mainly used as a lagging material due to their relatively low BET surface area and oil-absorbability.
U.S. Pat. No. 4,572,827, issued to G. Flemmert, describes a process for preparing finely-divided silicon dioxide by reaction of silicon fluoride in the vapor phase with water vapor, combustible gas and free oxygen-containing gas in a flame reaction zone to form hydrogen fluoride and silicon dioxide entrained in a gaseous reaction mixture and rapidly cooling the gaseous reaction mixture and entrained silicon dioxide to a temperature below 700.degree. C.
U.S. Pat. No. 4,790,486, issued to S. Eimaeda et al., discloses a process for preparing fine particles of hydrous silicic acid by neutralizing sodium silicate with sulfuric acid so that the proportion of particles having a particle size of 1 to 30 .mu.m is at least 80% and the proportion of particles having a particle size of at least 70 .mu.m is not more than 0.4%.
U.S. Pat. No. 4,629,508, issued to C. W. Cain Jr. et al., relates to a process for preparing hydrated calcium silicate, which process comprises reacting an aqueous slurry containing a source of calcium hydroxide, perlite as a source of silica, and a soluble calcium salt in the presence of high pressure saturated steam, then adding cooling water followed by subsequent venting of the reactor vessel to ambient pressure.